The present invention relates to bypass turbofan jet engines and, more particularly, relates to a high bypass-ratio turbofan jet engine having a plurality of non-coaxial fans.
As is well known in the art, turbofan jet engines are often used for aircraft propulsion. The turbofan jet engines generally include a turbine section that is designed to drive at least one compressor and a bypass fan. The bypass fan is typically a low-pressure compressor of large diameter, which is disposed upstream of the main compressor. The bypass fan is further arranged in coaxial relationship with a drive shaft or spool powered by the turbine.
Despite the popularity and successfulness of today""s turbofan jet engine, it is accurate to say that the current state-of-the-art in engine development is one of infinitesimally small improvements. Improvements in the art are often limited by the reluctance to modify such a successful design. However, in this regard it can be appreciated that there are structural limits imposed on today""s turbofan designs in light of current material advancements.
By way of background, turbofan jet engines typically have a coaxial design in that the bypass fan, the compressor, and the turbine sections rotate about a common axis on two or three coaxial shafts or spools. It is generally accepted that by increasing the bypass fan diameter or employing counter-rotating fans, one can improve the bypass ratio and, thus, the turbofan jet engine efficiency. However, there are number of disadvantages associated with these design techniques. For example, by increasing the bypass fan diameter, the diameter of the nacelle is also increased. The increased size of the nacelle in turn increases the drag and weight associated with the nacelle and the support strut.
Furthermore, the increased nacelle diameter may also cause ground clearance problems leading to undesirable configuration characteristics. Any type of oversized engine configuration inhibits the engines use in vertical take-off and landing designs. Still further, large diameter bypass fans further require extensive shielding in the event of a blade-out so as to contain the blades within the engine housing, also known as blade containment. Such blade containment requires robust materials that add significant weight to the aircraft. Alternatively, the addition of counter-rotating fans increases the complexity of the turbofan jet engine and further increases the buzz-saw noise from the front of the engine, which is undesirable.
During operation of conventional turbofan jet engines, it is necessary to shut down the engine in the event of a failure of the bypass fan stage. During the shutdown process, due to the sheer size of the bypass fan, the engine experiences very high blade-out loads further necessitating the aforementioned blade containment shielding.
Although conventional turbofan jet engines are quite safe and reliable, the efficiency of the design and associated components have been maximized. That is, the size, arrangement, and materials used generally limit further major advancements in turbofan jet engine design. Accordingly, in order to provide improved engine efficiency, there exists a need in the relevant art to change from the basic coaxially arranged turbofan jet engine design.
According to the principles of the present invention, a turbofan jet engine having an advantageous design is provided. The turbofan jet engine includes a housing and an engine core disposed in the housing. The engine core includes at least a compressor, turbine, and a drive shaft. The drive shaft defines a drive shaft axis. A plurality of fans are disposed in the housing and each is rotatable about a separate fan axis. Each of the fan axes are axially offset from the drive shaft axis. The turbofan jet engine further includes a drive system operably interconnecting the engine core and fans so as to rotatably drive the fans and selectively disengage select fans from the engine core.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.